A hot-rolled steel sheet after finish rolling of a continuous hot rolling process is, on a run-out table installed between the finish rolling mill and a winding apparatus, cooled to a predetermined temperature by a cooling apparatus provided above and below the run-out table, for example, and is then wound around the winding apparatus. In the hot rolling of the hot-rolled steel sheet, the cooling performance after finish rolling is an important factor in determining the mechanical properties, formability, weldability, etc. of the hot-rolled steel sheet, and it is important to uniformly cool the hot-rolled steel sheet to a predetermined temperature.
Hence, various methods and apparatuses have been conventionally proposed for this cooling of a hot-rolled steel sheet.
Patent Literature 1 proposes a method for cooling a hot strip, which is obtained after a hot rolling process, by bringing cooling water into contact with the hot strip, including: a first cooling step and a subsequent second cooling step, in which cooling is stopped at a strip temperature that is higher than a transition boiling start temperature in the first cooling step, and the cooling is conducted using the cooling water having a water flow density that causes nuclear boiling in the subsequent second cooling step. In addition, in the second cooling step, at least the upper surface of the strip is cooled by laminar cooling or jet cooling. Furthermore, in the second cooling step, the cooling water supplied to the upper surface of the strip is drained using water removing means, such as jet nozzles that eject a high-pressure fluid to the upper surface of the strip and a roll placed on the upper surface of the strip in its width direction.
Patent Literature 2 proposes a thick steel plate producing apparatus equipped with a conveyor line including a table roller that conveys a rolled thick steel plate from a roller to a hot leveler. Water spraying apparatuses that spray water on both surfaces of the steel plate are provided along the conveyor line at positions thereabove and therebelow. A roller exit-side water spray apparatus in which multiple cooling nozzles for spraying water are arranged along both outer sides of the conveyor line, upstream of the hot leveler of the conveyor line.
Patent Literature 3 proposes a cooling apparatus that jets cooling water to an upper surface of a hot-rolled steel sheet. On two positions in a longitudinal direction of the hot-rolled steel sheet, two cooling headers sandwiching the hot-rolled steel sheet in a width direction of the hot-rolled steel sheet are installed, namely four cooling headers are installed in total. From cooling nozzles attached to the respective cooling headers, cooling water is jetted toward the center of the four positions.
Patent Literature 4 proposes a cooling apparatus that cools hot-rolled steel material delivered from a finish rolling mill by supplying a coolant from a plurality of cooling banks. Nozzles for water removal are provided between the plurality of cooling banks, the nozzles for water removal being provided in both lateral sides in the width direction of the hot-rolled steel material, and high-pressure water is jetted to cross the width direction of the hot-rolled steel material.
Patent Literature 5 proposes a cooling apparatus that cools hot-rolled material travelling on a hot run table with cooling water in a curtain form falling from a slit nozzle of a cooling water header. Sprays are provided on both lateral sides of the hot run table, and pressure water jetted from each spray is directed so as to cross from the center part in the width direction of the hot-rolled material to an outer end. This pressure water from the sprays removes mutual interacting flow of cooling water occurring on the hot-rolled material.
Patent Literature 6 proposes a water removing method that removes cooling water jetted to a hot-rolled steel sheet when cooling the hot-rolled steel sheet before and after finish rolling, the water removing method including: removing cooling water by jetting water-removing water in a width direction of the hot-rolled steel sheet with a plurality of water removing nozzles that are aligned in a conveyance direction of the hot-rolled steel sheet on one lateral side or both lateral sides in a width direction of the hot-rolled steel sheet.